The present invention relates to a photosensitive resin composition and a circuit board. More particularly, the invention relates to a photosensitive resin composition suitable for use in forming an insulating layer for circuit boards, and a circuit board having an insulating layer obtained from the photosensitive resin composition.
Photosensitive poly(amic acid) resins containing a 1,4-dihydropyridine derivative as a photosensitizer are described in, e.g., JP-A-6-75376 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d), JP-A-7-271034, and JP-A-10-39510. Such a photosensitive poly(amic acid) resin is applied to a substrate and the resultant coating film is irradiated with actinic rays through a given photomask, subjected to exposure and development, and then imidized by heating, whereby a polyimide resin film of a given pattern can be formed.
Such photosensitive poly(amic acid) resins containing a 1,4-dihydropyridine derivative as a photosensitizer are excellent in sensitivity and resolution and the films of a given pattern obtained therefrom have high heat resistance. Because of this, these resins are used for forming insulating layers such as an interlayer dielectric and a surface protective layer (insulating protective layer) in circuit boards.
However, the photosensitive poly(amic acid) resins described in JP-A-6-75376 and JP-A-7-271034 have the following drawback. Since the 1,4-dihydropyridine derivative contained therein is insoluble in aqueous alkali solutions, development with an aqueous alkali solution alone results not only in a low rate of development but in precipitation of crystals of the 1,4-dihydropyridine derivative on the substrate or in the developing agent. If crystals of the 1,4-dihydropyridine derivative precipitate on the substrate, there is the possibility that precise pattern-wise development might be inhibited or recessed areas of the fine pattern formed through development might be partly filled up, resulting in reduced resolution. For developing such a photosensitive poly(amic acid) resin, it is therefore necessary to use as a developing solution a mixture of an aqueous alkali solution and a water-soluble organic solvent such as an alcohol.
On the other hand, the photosensitive poly(amic acid) resin described in JP-A-10-39510 contains a 1,4-hydropyridine derivative having enhanced solubility in aqueous alkali solutions and, hence, can be developed with an aqueous alkali solution alone. However, the rate of development thereof is still not fully satisfactory, and there is a desire for a photosensitive poly(amic acid) resin attaining a higher rate of development.
Furthermore, those photosensitive poly(amic acid) resins containing a 1,4-dihydropyridine derivative as a photosensitizer finally give a dark-colored (black-brown) film through imidization conducted at 300xc2x0 C. or higher. The conventional resins hence have a drawback that in the case where the film is used, e.g., as the surface protective layer of a circuit board, it is difficult to recognize the conductor circuit underlying the surface protective layer due to the dark color of the layer, making it difficult to inspect the appearance of the conductor circuit.
The invention has been achieved in view of these circumstances.
Accordingly, one object of the invention is to provide a photosensitive resin composition which is excellent in both sensitivity and resolution, can be rapidly developed with an aqueous alkali solution alone, further has excellent adhesion to substrates, and can give through imidization a light-colored polyimide resin film.
Another object of the invention is to provide a circuit board having an insulating layer obtained from the photosensitive resin composition.
In order to accomplish those objects, the invention provides a photosensitive resin composition which comprises a poly(amic acid) resin, a 1,4-dihydropyridine derivative represented by the following formula (1), and a polyethylene glycol: 
wherein Ar represents an aromatic group having a nitro group at an ortho position; R1 represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms; and R2, R3, R4, and R5 each represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.
The photosensitive resin composition may further comprise a polyhydric phenol compound.
The invention further provides a circuit board having an insulating layer obtained from either of the above photosensitive resin compositions, and a circuit board having a surface protective layer obtained from either of the above photosensitive resin compositions.